The Turbo code, an important channel coding method in the LTE, features high complexity and long time-delay in the coding & decoding, but excellent bit error performance. Therefore, it is suitable for the data transmission of the long code block (CB) with large quantities of data and with low time-delay requirements. The successful factors of the Turbo code lie in that: it can very well meet the randomicity condition in the Shannon's channel coding theory and it obtains coding gains by adopting the iterative decoding method, thus realizing the extreme performance approaching the Shannon limit.
FIG. 1 is a diagram of the structure of a Turbo decoder consisting of two soft-input soft-output (SISO) Recursive Systematic Convolutional (RSC) code component decoding units. The two units are connected through an interleaver and a deinterleaver for the iterative decoding. The extrinsic information apri1 output by the decoding unit 1 is used as the prior information of the decoding unit 2, and assists the decoding of the decoding unit 2. Likewise, the extrinsic information apri2 output by the decoding unit 2 is used as the prior information of the decoding unit 1. Iterative decoding is repeated in this way. The structures of the hardware of the decoding unit 1 and the decoding unit 2 are totally the same. During the hardware realization, time division multiplex can be used to save hardware resources. The decoding unit 1 and the decoding unit 2 are mainly to realize the Max-Log-Map algorithm of the data domain, wherein the multiplication and the exponent operation are simplified as the addition operation and the operation for taking the maximum, so as to reduce the computational complexity and facilitating the hardware realization. For the parallel Turbo decoder, the core is to set several parallel Max-Log-Map computing units in the decoding unit 1 and the decoding unit 2, so as to make the decoder perform segment decoding simultaneously for the data of the same CB.
The interleaver directly affects the performance of the Turbo decoder and plays a key role in the Turbo decoder. The interleaver adopted by the LTE is a Quadratic Permutation Polynomial (QPP) interleaver, which is one kind of Contention-free (CF) interleavers and whose expression is Π(i)=(f1·i+f2·i2)mod K (Formula 1-1), wherein i and Π(i) are the serial numbers before and after the interleaving, K is the CB length, and f1 and f2 are two parameters which can be specifically determined according to K, the CB length. That is, supposing the bit stream with a length K is c0, c1, . . . , ck-1 and the output of the interleaver is c′0, c′1, . . . , c′k-1, c′i can be expressed as c′i=cΠ(i).
The LTE system is required to support the peak data rate of over 100 Mbps, which puts forward higher requirements for the coding and decoding rate of the channel. To satisfy the requirements, the Turbo code in the LTE must adopt the parallel decoding algorithm. For the parallel decoding of the Turbo code, the design of the interleaver should also adapt to the requirements for the parallel decoding. The inventor found that in the related art, there is still no Turbo code interleaver or method capable of performing the parallel interleaving effectively.